Structure and regulation of the anthranilate synthase genes in Pseudomonas aeruginosa: I. Sequence of trpG encoding the glutamine amidotransferase subunit

We have determined the DNA sequence of the distal 148 codons of trpE andall of trpG in Pseudomonas aeruginosa. These genes encode, respectively,the large and small (glutamine amidotransferase) subunits of anthranilatesynthase, the first enzyme in the tryptophan synthetic pathway. Thesequenced region of trpE is homologous with the distal portion of E. coliand Bacillus subtilis trpE, whereas the trpG sequence is homologous to theglutamine amidotransferase subunit genes of a number of bacterial andfungal anthranilate synthases. The two coding sequences overlap by 23 bp.Codon usage in these Pseudomonas genes shows a marked preference for codonsending in G or C, thereby resembling that of trpB, trpA, and several otherchromosomal loci from this species and others with a high G + C content intheir DNA. The deduced amino acid sequence for the P. aeruginosa trpG geneproduct differs to a surprising extent from the directly determined aminoacid sequence of the glutamine amidotransferase subunit of P. putidaanthranilate synthase (Kawamura et al. 1978). This suggests that these twoproteins are encoded by loci that duplicated much earlier in the phylogenyof these organisms but have recently assumed the same function. We havealso determined 490 bp of DNA sequence distal to trpG but have notascertained the function of this segment, though it is rich in dyadsymmetries.